We have developed the first FDA lot release panel (HIV-2 Panel 1) for the detection of antibodies to HIV-2 only. In this study we characterizes the HIV-1 and HIV-2 antibody specificity's of these specimens using commercial enzyme-immunolinked Assays (EIA), Western blots (WB) and in-house antibody detection tests (Radio Immunoprecipitation, RIPA and Western blot and Dot blot, DB). Candidate sera were obtained from the CDC or purchased from commercial sources. Of 30 candidate specimens, six were non reactive on currently licensed HIV-1 EIA kits. Of these six, all reacted to ENV (gp105) and all but one to GAG (p26) by HIV-2 WB. All reacted to HIV-2 recombinant ENV and not HIV-2 ENV or HIV-1 GAG by DB. By HIV-2 RIPA all specimens reacted to a full range of ENV peptides (gp140, 105, 36) and very weakly to GAG peptides. Surprisingly, all but one specimen reacted to p24 on HIV-1 WB but did not react with licensed HIV-1 tests documented to contain p24 antigen. These studies suggest that the specificity of these specimens for HIV-2 antigens is primarily associated with reactivity to ENV and not GAG proteins. The lack of cross reactivity of these specimens for HIV-1 p24 in the EIA format maybe due to the way the GAG antigen is presented, that is non denatured verses denatured in the WB format. Future studies will try an confirm these observations and extend the hypothesis of conformational specificity to other retroviral antibody detection tests (i.e. HIV-1 and HTLV-I).